Systematic application of response spectral analysis and other analyses determine damping sensitivity of flight environment and candidate laboratory tests. Computerized comparison is made between response spectrum for flight environment, or enveloping spectra for collection of flight events, and response spectrum for candidate laboratory test

Cronin, D. L.

English

NASA Technical Reports Server

August 1971	 Brief 71-10266 
NASA TECH BRIEF 
Goddard Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield; Virginia 22151. Requests for individual copies or questions relating to the. Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Criteria for Vibration Testing 
A proposed approach for analyzing transient flight 
environments and specifying laboratory vibration 
tests to simulate these environments uses a sys-
tematic application of response spectra analysis, 
augmented by other analyses, to determine the 
damping sensitivity of both the flight environment 
and the candidate laboratory tests. 
A computerized comparison is made between the 
response spectrum for the flight environment, or an 
enveloping spectra for a collection of flight events, 
and the response spectrum for a candidate laboratory 
test. A ground rule for comparison is that the 
test spectrum must always exceed the flight spectrum. 
Within the context of this ground rule, parameters 
governing the test are varied to produce 'a minimum 
figure of merit indicating the best possible match 
of flight and test spectra. Other possible tests, e.g., 
sweeping sinusoidal vibration, rapid sine sweeps, 
and half-sine pulse shock tests, are similarly analyzed. 
Figures of merit for the optimum version of each 
test are then compared in order to determine which 
type of test best simulates the flight environment. 
Since damping for flight hardware is generally 
not well defined, a good laboratory test is one in 
which the optimized parameters based on the figure 
of merit determination change as little as possible 
when damping is varied in the spectral analysis. 
The trade-off between the magnitude of the figure 
of merit and the damping sensitivity of optimum 
parameters can be expected to produce a good 
laboratory test which is representative of the transient 
flight environment. 
With the method described, the conventional 
sine sweep test has proven to be less satisfactory 
for simulating a particular, but representative, 
set of flight transient environments, than has a 
transient-type test, e.g., a sum of decaying sinus-
oidals. However, because of its widespread use, 
conventional sine sweep testing, is investigated in 
detail, and a set of equations are provided, enabling 
the analyst to construct an accurate response 
spectrum which takes into account the reduction of 
peak response due to sweeping and the off-resonant 
response of systems having resonances outside the 
range of the sweep. 
Also treated was the question of whether or not a 
laboratory test and a flight transient having similar re-
sponse spectra produce similar responses in a space-
craft. Models of typical spacecraft were analyzed by 
computer, and the correlation between responses 
and figures of merit was quite good. The conclusion 
was that spectral methods are useful tools for the 
stated purpose, if applied carefully and systematically. 
Note: 
The following documentation may be obtained 
from:
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: 
NASA-CR-91356 (N68-12955), The Study 
of Mechanical Shock Spectra for Spacecraft 
Applications 
Patent status: 
No patent action is contemplated by NASA. 
Source: D. L. Cronin of

TRW Systems Group

under contract to

Goddard Space Flight Center

(GSC- 10137)
Category 06 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free frbm privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19710000265 2020-03-17T02:21:04+00:00Z


Criteria for vibration testing

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